outstanding segments = the segments that are sent and still not acknowledged
Base: the sequence number of the oldest unacknowledged packet
NextSeqNum: the sequence number of the first next packet to be sent
N: the size of the window
the receiver must deliver in-order bytes of data to the upper layer protocol
In GBN protocol,
out-of-order received segments are discarded. If the receiver expects a byte with SeqNum, but receives a byte with SeqNum + 1, it sends an ACK for byte SeqNum and discards the SeqNum+1 byte because it will be considered out of order. In other words, the receiver sends an ACK for each received in-order segment.
at the sender side, if the application layer gives data to the Transport layer whose sequence number is larger than base + N, TCP signals to the application that it rejected the data because the window is full.
Sender maintains only one timer. The timer starts with the oldest-sent-yet-not-acknowledged segment. With each ACK received, the Sender checks if there still are segments that are sent and not acknowledged. If so, the timer restarts. However, if there are no sent-yet-unacknowledged segments, the timer stops
if ACK for segment k is not received, then a timeout occurs and the sender retransmits all the segments up to the last sent-yet-not-acknowledged segment. For example, if the sender already sent segment 2 up to 5, and ACK 2 is not received, then in Go Back N the sender retransmits segments 2, 3, 4 and 5.
The following diagram describes the operations of the Go Back N protocol.
Call forwarding is one of the features of the call coverage in Cisco CUCM. Call Hunting is when CUCM distributes a call on more than one Directory Number (DN), whether consecutively or simultaneously, depending on the algorithm. Hunt Pilot A Hunt Pilot is the entry point for the whole call hunting process. It is hit by a Call. The Hunt Pilot number is a dialable entity and has many similarities with Route Patterns : We can configure Route Filters with Hunt Pilots, Hunt Pilots can Provide Outside Dial Tone , We can set Hunt Pilots with the Urgent Priority flag, They can route or block calls, They can apply Calling and Called Party Transformations. Hunt Lists After hitting the Hunt Pilot, the call is presented by CUCM to the Hunt List. Each Hunt List contains one or more ordered Line Groups. A Hunt List can be pointed by one or more Hunt Pilots. Line Groups Each Line Group contains one or more member (we’ll refer to them as Hunt members, hunt parties or Line Group members). A Line Grou...
Digit Signaling, aka Digit Addressing, is the method by which digits are sent from a dialing endpoint (e.g. phone) to a CUCM server, or by a voice gateway or trunk. There are three known digit signaling methods: En Bloc dialing SIP Dial Rules Digit-by-digit dialing 1. En Bloc digit dialing In the En Bloc digit signaling method, digits are sent as a whole block. Think of it like a brick that you send to UCM. This is the digit addressing method used on Type A Cisco phones, whether the endpoint signaling protocol is SIP or SCCP. En Bloc dialing is the default method used with the famous gateway protocols -MGCP, H323 and SIP- and also on H323 trunks and SIP trunks. Besides, the resulting pattern of a Translation Pattern operation is sent as En bloc to the call control system. 2. SIP Dial Rules It is important to know that all SIP phones support SIP dial rules, whether they are Type A or Type B. SIP dial rules are created on CUCM and downloaded by...
show voice port “show voice port” displays verbose information about all the voice ports on a voice gateway. Let’s examine “show voice port” on a E1 PRI gateway: On this gateway, we have two E1 PRI trunks, thus two voice ports. Each voice port is in the form “slot/subunit/port:signaling channel”. In the table that comes after each displayed voice port, we have 31 lines. These are the available channels on each PRI link. Notice that the column “CH” refers to timeslot, and not the channel. The 16th timeslot carries the 15th channel, which is the signaling channel (D channel). show voice port summary This command lists the voice ports and their timeslots combined into one table.
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