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Showing posts from January 11, 2009

DTMF Relay : RTP-NTE vs SIP INFO vs SIP NOTIFY

DTMF tones are the tones that are generated when a telephone key is pressed on a touchtone phone. Sometimes the called endpoint needs to hear those tones, such as when you enter digits during the call in response to a menu. Low-bandwidth codecs can distort the sound, however. DTMF relay allows that tone information to be reliably passed from one endpoint to the other. By default, SIP uses in-band signaling, sending the DTMF information in the voice stream. However, you can configure it to use RTP-NTE, SIP INFO messages, SIP NOTIFY messages, or KPML for transmitting DTMF tone information.

RTP-NTE is an in-band DTMF relay method, which uses RTP Named Telephony Event (NTE) packets to carry DTMF information instead of voice. If RTP-NTE is configured, SDP is used to negotiate the payload type value for NTE packets and the events that will be sent using NTE.

RTP-NTE can cause problems communicating with SCCP phones, which use only out-of-band DTMF relay. In a CallManager 4.x network with SCCP…

Media Termination Point (MTP)

A Media Termination Point (MTP) software device allows Cisco CallManager to relay calls that are routed through SIP or H.323 endpoints or gateways.

MTP, a Cisco software application, installs on a server during the software installation process. You must activate and start the Cisco IP Voice Media Streaming App service on the server on which you configure the MTP device. For information on activating and starting services, refer to the Cisco CallManager Serviceability Administration Guide.

Each MTP device that is defined in the database registers with the Media Resource Manager (MRM). The MRM keeps track of the total available MTP devices in the system and of which devices have available resources.

During resource reservation, the MRM determines the number of resources and identifies the media resource type (in this case, the MTP) and the location of the registered MTP device. The MRM updates its share resource table with the registration information and propagates the registered informa…

Super Group 3(SG3)

Super Group 3 (SG3) is a standard of fax machines that support speeds of up to 33.6 kbps through V.34 half duplex (HD) modulation and V.8 signaling.

Prior to Cisco IOS Release 12.4(4)T, SG3 fax machines could interoperate only over T.38 fax-relay and Cisco fax-relay networks with G3 fax machines, not with other SG3 fax machines, unless the fax machines were specifically configured to work at slower speeds or were configured for modem pass-through. The use of SG3 V.8 fax CM message suppression provides a gateway-controlled solution that enables SG3 fax machines to scale down without end-user interaction and without the extra bandwidth required by modem pass-through.

SG3 V.8 fax CM message suppression allows SG3 fax machines to interoperate over a fax-relay network at G3 speeds by blocking the SG3 V.8 CM message, or fax tone, from reaching the called fax machine. This causes the called fax machine to time out on the ANSam tone and scale down to G3 speeds by initiating V.21 negotiations.

Error Correction Mode(ECM)

Error correction mode (ECM) is an optional transmission mode built into Class 1 fax machines or fax modems. ECM automatically detects and corrects errors in the fax transmission process that are sometimes caused by telephone line noise. The page data is divided into what is known as Octets (small blocks of data).

Once the receiver has received all the Octets it examines them (using check-sums) and then advises the transmitting fax of any Octets that are in error. The transmitter then need only resend the blocks in error rather than the whole page. This generally means an ECM coded fax will be more likely to succeed on a noisy line. ECM is the norm rather than the exception. Some fax machines have the capability to enable or disable this function.

Changes to CCIE Lab and Written Exam Question Format and Scoring

看來大陸同胞們無法再飛到其他國家去考CCIE Lab來逃避CCIE Lab口試了,未來的CCIE Lab全面加上了口試至少可以保證CCIE的產出有一定的水平,不過這對東方人來說也許只是增加新的題庫而已,呵,事實上北京那邊的口試題目已經被大陸同胞們整理的差不多了,只要是有制式題目及答案的話,應該還是"上有政策,下有對策"。

Effective February 1, 2009, Cisco will introduce a new type of question format to CCIE Routing and Switching lab exams. In addition to the live configuration scenarios, candidates will be asked a series of four or five open-ended questions, drawn from a pool of questions based on the material covered on the lab blueprint. No new topics are being added. The exams are not been increased in difficulty and the well-prepared candidate should have no trouble answering the questions. The length of the exam will remain eight hours. Candidates will need to achieve a passing score on both the open-ended questions and the lab portion in order to pass the lab and become certified. Other CCIE tracks will change over the next year, with exact dates announced in advance.

Effective February 17th, 2009, candidates will also see two ot…