- #The ppp headers and trailers used to create a ppp frame how to
- #The ppp headers and trailers used to create a ppp frame plus
- #The ppp headers and trailers used to create a ppp frame mac
This technique has less value for large uncompressed voice packets. The bandwidth consumption for compressed voice packets can be reduced by nearly 60%. This technique actually compresses the RTP, UDP and IP headers and significantly reduces the RTP, UDP and IP overhead from 40 bytes to between 4 and 6 bytes. In other words, bigger packets are more efficient than smaller packets.Ĭisco has created a header compression technique that is now the standard called RTP header compression. As the size of the voice field gets larger with longer packets, the percentage of overhead decreases - therefore the needed bandwidth decreases. There are 54 bytes of overhead carrying the voice bytes. An IP PBX vendor may offer a standardized secure version of RTP (SRTP).
![the ppp headers and trailers used to create a ppp frame the ppp headers and trailers used to create a ppp frame](https://present5.com/presentation/59ad1807a1079247f7a18b8472dbd230/image-15.jpg)
Many implementations of RTP have no encryption, or the vendor has provided its own encryption facilities. This overhead can range from 20% to 80% of the bandwidth consumed over the LAN and WAN.
![the ppp headers and trailers used to create a ppp frame the ppp headers and trailers used to create a ppp frame](https://present5.com/presentation/59ad1807a1079247f7a18b8472dbd230/image-29.jpg)
#The ppp headers and trailers used to create a ppp frame plus
These headers, plus the Ethernet header, produce the overhead for shipping the packets. The Ethernet header and trailer account for another 18 bytes of overhead, for a total of at least 58 bytes of overhead before there are any voice bytes in the packet. The RTP plus UDP plus IP headers will add on 40 bytes. The header and trailer overhead can be called the shipping and handling cost. The headers and trailers are required fields for the networks to carry the packets. It is really voice over RTP, over UDP, over IP and usually over Ethernet. The Ethernet header is replaced with a frame relay, ATM or PPP header and trailer when the packet enters a WAN. The Ethernet trailer is used for error detection purposes.
#The ppp headers and trailers used to create a ppp frame mac
The Ethernet header carries the LAN MAC addresses of the sending and receiving devices. The IP header carries the sending and receiving IP addresses for the call plus other control information. The UDP header carries the sending and receiving port numbers for the call. The digitized voice field can contain as few as 10 bytes of compressed voice or as many as 320 bytes of uncompressed voice. The packet rate is 50 packets per second for 20ms and 33.3 packets per second for 30ms voice samples.The voice packets are transmitted at these fixed rates. The digitized voice field, RTP, UDP and IP headers remain the same.Įach of these packets will contain part of a digitized spoken word. RTP can be carried on frame relay, ATM, PPP and other networks with only the far right header and left trailer varying by protocol. The RTP packet format for VoIP over Ethernet is shown below.
![the ppp headers and trailers used to create a ppp frame the ppp headers and trailers used to create a ppp frame](https://images.slideplayer.com/19/5783816/slides/slide_17.jpg)
The content descriptor defines the compression technique (if there is one) used in the packet. The RTP header field contains the digitized speech sample (20 or 30ms of a word) time stamp and sequence number and identifies the content of each voice packet. Many vendors have chosen 20 or 30ms size packets. Longer packets that contain more speech bytes reduce the bandwidth requirements but produce a longer construction delay and are harder to fix if lost. Short packets require more bandwidth, however, because of increased packet overhead (this is discussed below). Shorter packets cause less of a problem if the packet is lost. The shorter the packet creation delay, the more network delay the VoIP call can tolerate. The shorter the packet, the shorter the delayĮnd-to-end (phone-to-phone) delay needs to be limited. As you have already figured out, it takes many packets to carry one word. This does not matter to the RTP protocol. The 10 to 40ms of digitized speech can be uncompressed, compressed and even encrypted. It is the commonly used protocol among IP PBX vendors.Īn IP phone or softphone generates a voice packet every 10, 20, 30 or 40ms, depending on the vendor's implementation. RTP will work with any signaling protocol. RTP is an IETF standard introduced in 1995 when H.323 was standardized. The Real-Time Transport Protocol (RTP) carries speech transmission. VoIP requires two classes of protocols: a signaling protocol such as SIP, H.323 or MGCP that is used to set up, disconnect and control the calls and telephony features and a protocol to carry speech packets. Voice over IP (VoIP) is the descriptor for the technology used to carry digitized voice over an IP data network.
#The ppp headers and trailers used to create a ppp frame how to
This guide investigates what bandwidth means for VoIP, how to calculate bandwidth consumption for a VoIP network and how bandwidth can be saved by using voice compression Bandwidth requirements for Voice over IP can be a tricky beast to tame until you look at the method and factors involved.