QoS & VoIP - Quality of Service

Everyone can use VoIP by yahoo messager right ? but how about the quality ? it is bad and it is difficult to hear.
Tuy luc co luc it traffic nhu ban dem thi co the nghe duoc chut dinh va co khi traffic nhieu thi khong nghe duoc vi ly do rat de hieu. Khi tat ca moi nguoi neu noi qua IP layer 3 va TCp layer 4
cua OSI moi nguoi noi voi internet deu co quyen uu tien nhu nhau. Thi du doc email hay goi 1 file di hay noi chuyen voi IP thi deu co quyen uu tien nhu nhau.
Co mot dieu IP packet for voice rat ngan va nhieu goi nhu vay lien tuc khong bi dut doan thi moi co the noi chuyen duoc de dang. Thi du: "Anh di dau ?" co the chia lam 3 goi IP packet vi
time out cua IP rat nhanh ma minh thi noi chuyen cham hon.
Day la IP header
4 bit version + 4 bit header length + 8 bit type of Service (TOS)+ 16 bit lenght [32 bit]
16 bit identification + 3 bit flags + 13 bit fragment offset [32 bit]
8 bit time to live (TTL) + 8 bit protocol + 16 bit checksum [32 bit]
32 bit source IP address [32 bit]
32 bit destination address[32 bit]
data [ up 65535 bytes] (de hieu vi 16-bit lenght = 1111111111111111(hex-FFFF) - header = 65535
anh di dau: packet 1 + packet 2 + packet 3
(neu khong co uu tien thi 3 goi nay se den muc tieu destination thoi diem rat khac nhau nhieu,
su khac biet nay se KHONG thay ro rang khi goi email hay file upload nhung voice thi nghe se phan biet duoc vi vay QoS nam vai tro rat quan trong Voice over IP, thoi gian cua 3 packets nay di chuyen tu source den destination khong quan trong ma quan trong 3 packets co den cung luc hay khong chac chan se co delay vi co the di rat xa vi du Ottawa->Atlanta->California->HongKong ->VN, you can do "tracert vinetcom.com" from Vietnam you will will see how many hops that the packet is passed, that is fine this is the whole idea of the internet)
Vi moi nguoi co quyen uu tien nhu nhau den goi thu 3 (packet 3) co the den rat tre vi vay cuon dam thoai bi gian doan. MUON NGHE DUOC THI FAI TRA TIEN de co duoc QoS (quality of service) rat de hieu server truoc khi goi IP thi gang vao TOS thi goi IP nay tro thanh uu tien. Tuy theo tien tra co 3 loai (class) gom co Gold (vang), Silver (bac) va Bronze (Dong)
Day la nhiem vu chinh cua DiffServ. DiffServ differented the services, it is a method of trying to guaranteed quality of service on the large network such as an internet.