Showing posts from November 11, 2007

Gatekeeper-Routed Call Signaling(GKRCS) vs Direct Endpoint Signaling

There are two types of gatekeeper call signaling methods:

Direct Endpoint Signaling
—This method directs call setup messages to the terminating gateway or endpoint.

Gatekeeper-Routed Call Signaling (GKRCS)
—This method directs the call setup messages through the gatekeeper.

Note: Cisco IOS gatekeepers are Direct Endpoint signaling based and do not support GKRCS.

These diagrams illustrate the differences between these two methods:

Back-to-back user agent(B2BUA)

From Wikipedia, the free encyclopedia

The Back-to-Back User Agent (B2BUA) acts as a user agent to both ends of a Session Initiation Protocol (SIP) call. The B2BUA is responsible for handling all SIP signalling between both ends of the call, from call establishment to termination. Each call is tracked from beginning to end, allowing the operators of the B2BUA to offer value-added features to the call.

To SIP clients, the B2BUA acts as a User Agent server on one side and as a User Agent client on the other (back-to-back) side. The basic implementation of a B2BUA is defined in RFC 3261. The B2BUA may provide the following functionalities:

call management (billing, automatic call disconnection, call transfer, etc.) network interworking (perhaps with protocol adaptation) hiding of network internals (private addresses, network topology, etc.) codec translation between two call legs
Because it maintains call state for all SIP calls it handles, failure of a B2BUA affects all these calls. Often, B…


The dejitter buffer size determines the ability of the emulated circuit to tolerate network jitter. The dejitter buffer in CEoIP software is configurable up to 500 milliseconds; the maximum amount of network jitter that CEoIP can tolerate is ±250 milliseconds.

dejitter-buffer size
Router(config-cem)# dejitter-buffer 80

(Optional) Specifies the size of the dejitter buffer used to compensate for the network filter.
Use the size argument to specify the size of the buffer in milliseconds. Default is 60.

Quality of Service Options on GRE Tunnel Interfaces

The qos pre-classify command

When packets are encapsulated by tunnel or encryption headers, QoS features are unable to examine the original packet headers and correctly classify the packets. Packets traveling across the same tunnel have the same tunnel headers, so the packets are treated identically if the physical interface is congested. With the introduction of the Quality of Service for Virtual Private Networks (VPNs) feature, packets can now be classified before tunneling and encryption occur.

In the following example, tunnel0 is the tunnel name. The qos pre-classify command enables the QoS for VPNs feature on tunnel0:

Router(config)# interface tunnel0
Router(config-if)# qos pre-classify

Characterizing Traffic for QoS Policies

When configuring a service policy, you first may need to characterize the traffic that is traversing the tunnel. Cisco IOS supports Netflow and IP Cisco Express Forwarding (CEF) accounting on logical interfaces like tunnels. See the NetFlow Services Solutions Guid…

Cisco Security Device Manager(SDM) three categories

The Cisco SDM QoS wizard offers easy and effective optimization of LAN, WAN, and VPN bandwidth and application performance for different business needs (for example, voice and video, enterprise applications, and web). Three predefined categories are:

1. Real-time
2. Business-critical
3. Best-effort

In addition, the Cisco SDM QoS wizard supports NBAR, which provides real-time validation of application usage of WAN bandwidth against predefined service policies as well as QoS policing and traffic monitoring.

Police vs Shape

Policing can be applied to either the inbound or outbound direction, whileshaping can be applied only in the outbound direction.Policing drops nonconforming traffic instead ofqueuing the traffic like shaping.

Policing also supports marking of traffic. Traffic policing is more efficient in terms of memory utilization than traffic shaping because no additional queuing of packets is needed.

Both traffic policing and shaping ensure that traffic does not exceed a bandwidth limit, but each mechanism has different impacts on the traffic:

1. Policing drops packets more often, generally causing more retransmissions of connection-oriented protocols, such as TCP.

2. Shaping adds variable delay to traffic, possibly causing jitter. Shaping queues excess traffic by holding packets in a shaping queue.

Traffic shaping is used to shape the outbound traffic flow when the outbound traffic rate is higher than a configured rate. Traffic shaping smoothes traffic by storing traffic above the configured rate in a…

Processing vs Queuing vs Serialization vs Propagation vs End-to-End delay

1. Processing delay:
The time that it takes for a router (or Layer 3 switch) to take the packet from an input interface and put it into the output queue of the output interface. The processing delay depends on various factors:
CPU speed CPU utilization IP switching mode Router architecture Configured features on both the input and output interfaces 2. Queuing delay:
The time that a packet resides in the output queue of a router. Queuing delay depends on the number of packets already in the queue and their sizes. Queuing delay also depends on the bandwidth of the interface and the queuing mechanism.

3. Serialization delay:
The time that it takes to place a frame on the physical medium for
transport. This delay is typically inversely proportional to the link bandwidth.

4. Propagation delay:
The time that it takes for the packet to cross the link from one end to the other. This time usually depends on the type of media. (For example, satellite links produce the longest propagation delay because …

Convert Digital Signals to Analog Signals Steps

Step 1 Decompression:
If the voice signal was compressed by the sender, it is first decompressed.

Step 2 Decoding:
The received, binary formatted voice samples are decoded to the amplitude value of the samples. This information is used to rebuild a PAM signal of the original amplitude.

Step 3 Reconstruction of the analog signal:
The PAM signal is passed through a properly designed filter that reconstructs the original analog wave form from its digitally coded counterpart. The whole process is simply the reverse of the analog-to-digital conversion. Like analog-to-digital conversion, digital-to-analog conversion is performed by DSPs, which are located on the voice interface cards. The conversion is needed for calls being received from a packet network or digital interfaces, which are then transmitted out an analog voice interface.

FXS vs FXO vs E&M

Gateways use different types of interfaces to connect to analog devices, such as phones,
fax machines, or PBX or public switched telephone network (PSTN) switches. Analog
interfaces used at the gateways include these three types:

The FXS interface connects to analog end systems, such as analog phones or
analog faxes, which on their side use the FXO interface. The router FXS interface
behaves like a PSTN or a PBX, serving phones, answering machines, or fax machines
with line power, ring voltage, and dial tones. If a PBX uses an FXO interface, it can also
connect to a router FXS interface. In this case, the PBX acts like a phone.

The FXO interface connects to analog systems, such as a PSTN or a PBX, which
on their side use the FXS interface. The router FXO interface behaves like a phone,
getting line power, ring voltage, and dial tones from the other side. As mentioned, a PBX
can also use an FXO interface toward the router (which will then use an FXS interface),
if the PBX takes the role of…

Convert Analog Signals to Digital Signals Steps

Step 1 Sampling:
The analog signal is sampled periodically. The output of the sampling is a pulse amplitude modulation (PAM) signal.

Step 2 Quantization:
The PAM signal is matched to a segmented scale. This scale measures the amplitude (height) of the PAM signal.

Step 3 Encoding:
The matched scale value is represented in binary format.

Step 4 Compression:
Optionally, voice samples can be compressed to reduce bandwidth requirements. Analog-to-digital conversion is done by digital signal processors (DSPs), which are located on the voice interface cards. The conversion is needed for calls received on analog lines, which are then sent out to a packet network or to a digital voice interface.

Service-Provider CCIE Written 補充資料整理完結

經過了兩三個月的時間,我儘了最大的努力找出所有SP CCIE Written可能相關"主題"的文章摘要,並且用紅色字體標註"重點",希望對各位了解題意有幫助,順便可以知道原來的文章出處及更詳盡的內容意義。

今天已經完成了第一階段的SP CCIE Written考試,接下來就是要準備第二階段SP CCIE Lab的部份了,我會邊作Lab邊將個人心得紀錄在這個blog中,希望我的經歷可以讓各位更輕鬆地準備SP CCIE!

祝各位CCIE Candiates好運! 一起克服大魔王!

Why Are Some OSPF Routes in the Database but Not in the Routing Table?

A common problem when using Open Shortest Path First (OSPF) is routes in the database don't appear in the routing table. In most cases OSPF finds a discrepancy in the database so it doesn't install the route in the routing table. Often, you can see the Adv Router is not-reachable message (which means that the router advertising the LSA is not reachable through OSPF) on top of the link-state advertisement (LSA) in the database when this problem occurs. Here is an example:

Adv Router is not-reachable
LS age: 418
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID:
Advertising Router:
LS Seq Number: 80000002
Checksum: 0xFA63
Length: 60
Number of Links: 3

There are several reasons for this problem, most of which deal with mis-configuration or a broken topology. When the configuration is corrected the OSPF database discrepancy goes away and the routes appear in the routing table. This document explains some of the more common reasons that…

專家輕鬆駭入XP 微軟高層震攝

CNET新聞專區:Tom Espiner

2007/11/14 13:43

兩位英國電子犯罪專家僅利用幾分鐘的時間就駭入一台未受保護的Windows XP主機,並連結一個不安全的無線網路,讓親眼目睹的微軟公司高層大感「震攝」。

由英國政府和產業界贊助的網路安全活動Get Safe Online,12日邀請了兩位任職於英國重大組織犯罪局(Serious Organized Crime Agency)的專家,示範如何將一台使用Windows XP及Service Pack 1的電腦,連上一個不安全的無線網路。這台主機沒有任何防毒軟體、防火牆或反間諜軟體機制,並有一個內含密碼的檔案,作為示範偷竊的目標。



Mick用XP Wireless Network Connection Status(無線網路連線狀態)對話窗找到他自己電腦的IP位址,再用數字推演法,將前後一定範圍的IP位址輸入攻擊工具,尋找其中是否有未受保護的主機。


連上不安全的無線網路後,刺探網路上其他電腦可能的IP位址,他找到了Andy未受保護的電腦。接著,他掃瞄開放的入口,用攻擊工具建立刺探程式,再以惡意軟體駭入XP系統的command shell,此時只花了6分鐘。

SOCA電子犯罪組副主任Sharon Lemon表示:「如果你是坐在(一家有Wi-Fi網路的咖啡廳裡),你的咖啡甚至還沒變涼呢。」



AOL一週進行2次收購 拿下社交搜索網Yedda

發佈時間:2007.11.13 07:54 來源:賽迪網 作者:天虹


AOL首席運營官Ron Grant稱,把Yedda獨特的技術結合到AOL能夠使我們把我們傳統的搜索資源與整個社區的人聯繫起來,幫助用戶快速找到答案。



Traffic Engineering

To demonstrate how traffic engineering addresses the problem of underutilized links, we will take an example in Figure 3-18 by first defining the traffic engineer terminology:
Head-End—A router on which a TE tunnel is configured (R1) Tail-End—The router on which the TE tunnel terminates (R3) Mid-point—A router through which the TE tunnel passes (R2) LSP—The label-switched path taken by the TE tunnel; here it's R1-R2-R3 Downstream router—A router closer to the tunnel tail Upstream router—A router farther from the tunnel tail (so R2 is upstream to R3's downstream, and R1 is upstream from R2's downstream) Continuing the traffic engineering building block, information distribution is done via a link state protocol, such as IS-IS or OSPF. The link state protocol is required only for traffic engineering, not for the implementation of Layer 3 VPNs. A link state protocol is required to ensure that information gets flooded and to build a topology of the entire network.


Resilient Packet Ring Feature Guide

IEEE 802.17 Resilient Packet Ring Feature Guide

This feature guide describes how to configure the Cisco implementation of the IEEE 802.17 Resilient Packet Ring (RPR) protocol on supported Cisco routers and includes information about the benefits of the feature, supported platforms, related publications, and so on. RPR is similar but not identical to the Spatial Reuse Protocol (SRP), the underlying technology used in the Cisco Dynamic Packet Transfer (DPT) family of products. Throughout this document, this feature is referred to as RPR.

This document covers the use of the RPR feature. It does not include hardware installation and initial configuration information. Refer to the appropriate router installation and configuration note for information on how to configure the hardware and prepare it for use with RPR.

Information About RPR
Resilient Packet Ring (RPR), as described in IEEE 802.17, is a metropolitan area network (MAN) technology supporting data transfer among stations interconnecte…

RFC4170 - Tunneling Multiplexed Compressed RTP (TCRTP)

Mandatory AVP's:
Message Type
Assigned Session ID
Call Serial Number

QoS Requirements of Video

Two main types of video traffic exist: Interactive-Video (videoconferencing) and Streaming-Video (both unicast and multicast). Each type of video is examined separately.

When provisioning for Interactive-Video (video conferencing) traffic, the following guidelines are recommended:

Interactive-Video traffic should be marked to DSCP AF41; excess videoconferencing traffic can be marked down by a policer to AF42 or AF43. Loss should be no more than 1 percent.One-way latency should be no more than 150 ms. Jitter should be no more than 30 ms.Assign Interactive-Video to either a preferential queue or a second priority queue (when supported); when using Cisco IOS LLQ, overprovision the minimum-priority bandwidth guarantee to the size of the videoconferencing session plus 20 percent. (For example, a 384-kbps videoconferencing session requires 460 kbps of guaranteed priority bandwidth.)

OSPF Sham-Link Support for MPLS VPN

Using OSPF in PE-CE Router Connections

In an MPLS VPN configuration, the OSPF protocol is one way you can connect customer edge (CE) routers to service provider edge (PE) routers in the VPN backbone. OSPF is often used by customers that run OSPF as their intrasite routing protocol, subscribe to a VPN service, and want to exchange routing information between their sites using OSPF (during migration or on a permanent basis) over an MPLS VPN backbone.

Figure 1 shows an example of how VPN client sites that run OSPF can connect over an MPLS VPN backbone.

Figure 1 OSPF Connectivity Between VPN Client Sites and an MPLS VPN Backbone

When OSPF is used to connect PE and CE routers, all routing information learned from a VPN site is placed in the VPN routing and forwarding (VRF) instance associated with the incoming interface. The PE routers that attach to the VPN use the Border Gateway Protocol (BGP) to distribute VPN routes to each other. A CE router can then learn the routes to other sites in the…

IP Event Dampening

The IP Event Dampening feature introduces a configurable exponential decay mechanism to suppress the effects of excessive interface flapping events on routing protocols and routing tables in the network. This feature allows the network operator to configure a router to automatically identify and selectively dampen a local interface that is flapping.

Restrictions for IP Event Dampening
Subinterface Restrictions
Only primary interfaces can be configured with this feature. IP Event Dampening does not track the flapping of individual subinterfaces on an interface.

Virtual Templates Not Supported
Copying a dampening configuration from virtual templates to virtual access interfaces is not supported because dampening has limited usefulness to existing applications that use virtual templates. Virtual access interfaces are released when an interface flaps, and new connections and virtual access interfaces are acquired when the interface comes up and is made available to the network. Since dampening…



The primary goal of QoS is to provide priority for traffic flows to and from specific devices. In this context, priority means providing lower latency and higher bandwidth connections with more controlled jitter.

An underlying principle of Fibre Channel switching is that the network guarantees that no frames will be dropped. If this is the case, why do we need QoS at all?

Switches today provide high-performance, non-blocking, non-oversubscribed crossbar switch fabrics. The Cisco MDS 9513 Multilayer Director can switch more than a billion frames per second. Why would users ever need QoS when a switch fabric provides seemingly endless amounts of frame-switching capacity?
The answer is simple: congestion.

Congestion occurs for two basic reasons:
• Congestion will occur if multiple senders are contending with a smaller number of receivers. If the aggregate rate of traffic transmitted by senders exceeds the size of the connection to the receivers, blocking will occur (Figure 1…

MPLS AToM: Overview

Feature Overview
Any Transport over MPLS (AToM) is a solution for transporting Layer 2 packets over an MPLS backbone. AToM enables service providers to supply connectivity between customer sites with existing data link layer (Layer 2) networks by using a single, integrated, packet-based network infrastructure — a Cisco MPLS network. Instead of separate networks with network management environments, service providers can deliver Layer 2 connections over an MPLS backbone.

With Cisco AToM technology, provisioning and connecting is straightforward. A customer using Ethernet in a building or campus in one location can connect through a service provider offering Ethernet over MPLS to the customer's Ethernet networks in remote locations.

AToM provides a common framework to encapsulate and transport supported Layer 2 traffic types over an MPLS network core. Service providers can use a single MPLS network infrastructure to offer customers connectivity for supported Layer 2 traffic, as well as…

L2TPv3 Enables Layer 2 Services for IP Networks

White Paper


Layer 2 Tunneling Protocol Version 3
Enables Layer 2 Services for IP Networks
The competitive environment for service providers has changed considerably since the Internet became a global force in the 1990s. Enterprises are no longer signing up for new IP-based services for the novelty or out of fear of being left behind by the competition. The challenge for service providers today is to grow their businesses by expanding their customer base and service revenue in a more cautious spending environment. Most enterprises are taking a more conservative approach to network investments. New IP-based services give enterprises an opportunity to improve their productivity and competitiveness while lowering their existing network expenses. Service providers that offer these services and savings can grow their customer base and service revenue. This white paper focuses on one such opportunity—offering tradit…

Cisco Nonstop Forwarding for BGP: Deployment & Troubleshooting

1.0 Overview
Cisco Nonstop Forwarding with Stateful Switchover (NSF with SSO) is a Cisco innovation for routers with dual route processors. Cisco NSF with SSO allows a router that has experienced hardware or software failure of an active route processor to maintain data link layer connections and continue forwarding packets during the switchover to the standby route processor. This forwarding can continue despite lost routing protocol peering arrangements with other routers. Routing information is recovered dynamically, in the background, while packet forwarding proceeds uninterrupted.

Cisco NSF for BGP is a combination of internal system modifications to the various NSF-capable hardware platforms, and external enhancements to the BGP-4 protocol. The modifications to the BGP protocol (BGP Graceful Restart) have been submitted to the Internet Engineering Task Force (IETF):

This document will detail specific changes to the B…